The present invention relates to image forming apparatuses including a copying machine of an electrophotographic system, a printer and a facsimile machine, each being equipped with an LED (Light Emitting Diode) printing head.
In the image forming apparatuses such as a copying machine, a printer and a facsimile machine, each being of a digital form employing an electrophotographic technology, a laser beam and an LED array are commonly used as an exposing unit for a photoreceptor.
In the case of exposure by means of a laser beam, an exposure method used normally is one wherein a laser beam prepared by a semiconductor laser, a plurality of lenses and by a polygon mirror (rotary polygonal mirror) is oscillated in the direction perpendicular to the direction of rotation of the photoreceptor for conducting exposure.
On the other hand, with respect to exposure by means of an LED array, in the exposure method used commonly, an LED printing head that houses a base plate having therein a plurality of LEDs arranged linearly (LED array) and IC that drives the LEDs and housing a columnar lens array provided on the front side of the LED array in one outer package is arranged in the direction perpendicular to the direction of rotation of the photoreceptor to be close to the photoreceptor surface, and lighting of the LED at a prescribed position is controlled for exposure.
An exposing unit employing the LED printing head is advantageous in terms of low noise and compactness, because no component operating mechanically like a polygon mirror is in existence therein, in comparison with an exposing unit employing a laser beam. However, in the exposing unit, there is a risk of deterioration of the tip of the columnar lens array representing the tip of the LED printing head caused by ozone generated from a charging electrode of a charger, and there is also a fear that toner scattering from a developer representing a developing unit may adhere to the tip of the columnar lens array.
For eliminating these problems of the LED printing head, there are proposals including one to provide a mechanism to create an air flow on the tip of the LED printing head (for example, see Japanese Patent Application Publication No. 05-177864 (FIG. 1 on the first page)) and the other for providing a dustproof shutter (for example, see Japanese Patent Application Publication No. 2004-191477 (first page-third page)).
However, a complicated mechanism of the LED printing head often complicates maintenance work for removing dust when dust such as toner adheres to the LED printing head, which may result in a fear of a cost increase of the LED printing head itself.